I often travel for as much as 3 mos in Europe and so that means taking a huge supply of prescription drugs; I have never had anyone at immigration or security take the slightest notice of them. I always carry them in the messenger bag I also use for the computer, camera, phone etc on the plane. As others have noted, never pack this stuff in checked luggage. I don't have any drugs prone to abuse except maybe Ambien which I leave in its prescription bottle. If you have narcotics, injectables etc it is probably prudent to have medical documentation.
We always pack the OTC meds in the checked luggage; France has excellent pharmacists who are the first line in health care and most pharmacies have at least one person who can speak a bit of English and can counsel you if you need a particular OTC drug or sometimes even prescription drugs. We have had statins my husband forget to pack replaced without prescription; pharmacists have some discretion on such things. With OTC meds it is helpful to have the chemical name; I have always been able to get what I need with that e.g. things like decongestants, cough medicines etc. If you take a lot of such things as ibuprofen, bring your own supply as these are oddly expensive in Europe and sold in very small quantities; generally meds are much cheaper particularly prescription drugs.
Oxygen seems like a bigger issue on both plane and to replace. I would assume you have to make special arrangements to take it through security and carry it on board and make sure that whatever is available in France will fit the connectors and such. That is specialized information I don't have but you need to run down.